处理器类

public class Cpu {
    public void start() {
        System.out.println("处理器启动了...");
    }
}

内存类

public class Memory {
    public void start() {
        System.out.println("内存启动了...");
    }
}

硬盘类

public class Disk {
    public void start() {
        System.out.println("硬盘启动了...");
    }
}

电脑类

public class Computer {
    private Cpu cpu;
    private Memory memory;
    private Disk disk;

    public void start() {
        System.out.println("电脑启动中...");

        cpu.start();
        memory.start();
        disk.start();

        System.out.println("电脑启动完毕");
    }
}

演示类

public class Demo {
    public static void main(String[] args) {
        Computer computer = new Computer();

        computer.setCpu(new Cpu());
        computer.setMemory(new Memory());
        computer.setDisk(new Disk());

        computer.start();
    }
}

演示结果